1. Field of the Invention
The invention relates to a structure of an articulated vehicle, such as a riding lawn mower, comprising two mutually pivotally connected front and rear frames equipped with respective transaxle apparatuses supporting axles with wheels mounted thereon. More particularly, it relates to a structure for transmitting driving force to the transaxle apparatuses of both the frames from a prime mover, a structure for transmitting driving force from the prime mover to a working device attached to one of the frames, and a structure with a coupling part of the front and rear frames.
2. Related Art
Conventionally, there is a well-known articulated riding lawn mower having mutually pivotally connected first and second frames so as to enable the first frame to turn relative to the second frame. The first frame is disposed at one of front and rear portions of the vehicle and equipped with a prime mover and a transaxle apparatus which supports axles driven by power from the prime mover. On the other hand, the second frame is disposed at the other of the front and rear portions of the vehicle and equipped with a working device (such as a mower device), an operating section, and an axle casing that supports freely rotatable axles.
Japanese Patent Laid Open Gazette 2000-270651 discloses an articulated four-wheeled lawn mower, which comprises the first frame as a rear frame and the second frame as a front frame. On the rear frame is disposed an HST (a hydrostatic transmission), which transmits engine power to rear wheels supported on the rear frame. Moreover, in the rear frame is disposed a power take-off shaft which takes out power from a pump shaft of a hydraulic pump of the HST which rotates synchronously to the engine power output rotation. The rotation of the pump shaft is transmitted to a mower device supported by the front frame.
Generally, as to each of the vehicles having the above structure, while the axles supported by the transaxle apparatus of the first frame usually serving as a rear frame is driven by the prime mover, the axles supported by the axle casing of the second frame usually serving as a front frame rotate freely in no association with the power for driving the axles of the first frame. Thus, the vehicle is of the so-called two-wheel (rear-wheel) drive type.
However, the two-wheel drive vehicle which drives only rear wheels is inferior in its gradablility when working on a slope and roadability when running on a bad road. There arise some problems such that the vehicle, when being in mud etc., is hard to bail out. For solving the problems, the articulated vehicle is desired to become a four-wheel drive vehicle, which drives both its front and rear wheels.
The rear frame of the vehicle disclosed in the document is provided with the HST and the power take-off shaft for taking out power for the working device. However, as mentioned above, the power take-off shaft rotates synchronously with rotation of the pump shaft, which is fixed in speed as long as engine speed is fixed. On the other hand, the rotary speed of the rear wheels, which are driven by power output of the hydraulic motor, is variable according to running-speed-changing operation for adjusting the angle of a movable swash plate of the hydraulic pump. Therefore, the power take-off shaft for driving the working device cannot be used as a front wheel drive shaft as it is.
Moreover, even if the power for driving the front wheels can be transmitted to the front frame from the rear frame so as to rotate the front wheels synchronously to the rotation of the rear wheels, the lawn mower disclosed in the document also requires means to transmit the power of the prime mover carried in the rear frame to the working device provided on the front frame. For this reason, existence of the coupling part between the rear frame and the front frame complicates the configuration of the power transmitting system of these two trains.